The present invention relates to a wax type thermostat for controlling temperature of a coolant of an automotive engine.
Referring to FIG. 6 showing a conventional cooling system for an automotive engine, the system has a thermostat 1 which is disposed in an inlet side passage of water jackets 20.
The cooling system comprises a first coolant passage 24 disposed between an upper outlet 21 of the water jackets 20 and an upper inlet 23 of a radiator 22, and a second coolant passage 30 provided between a lower outlet 25 of the radiator 22 and a lower inlet 29 of the water jackets 20, including a thermostat cap 26, a thermostat housing 27 and a water pump 28. A bypass passage 31 is provided between a junction J of the first passage 24 and the thermostat housing 27 so as to communicate the first passage 24 with the second passage 30 without passing the radiator 22. The thermostat 1 is hermetically secured to the housing 27 by the thermostat cap 26. The thermostat 1 has a main valve 12 for closing the second passage 30 and a bypass valve 15 for closing a bypass port 32 of the bypass passage 31.
In FIG. 6, the reference A' designates a measuring point for measuring the temperature of the coolant in the housing 27, and B' designates a measuring point provided in the second passage 30 adjacent to the thermostat cap 26 and upstream of the thermostat 1 for measuring the temperature of the coolant in the second passage 30. The reference C designates a measuring point for measuring the flow rate of the coolant in the second passage 30. The reference numeral 33 designates a cooling fan.
The thermostat 1 is operated by a thermo-actuator. The thermo-actuator comprises an actuating steel rod and a resilient seal spool which is slidably engaged with the rod. The seal spool is inserted in a heat sensitive cylinder filled with wax pellets.
As shown in FIG. 7, a perforation 19a is formed in a flange 16 of the thermostat 1, and a jiggle valve mechanism 17 having a jiggle valve 18 is movably engaged in the perforation 19a.
During the operation of the engine, the jiggle valve 18 is closed by the pressure of the coolant in the second coolant passage 30 as shown in FIG. 7. When the engine stops, the jiggle valve opens. Thus, the coolant can be supplemented in the direction of the arrow.
During the cold engine state, the main valve 12 of the thermostat 1 is closed as shown in FIG. 6, and the jiggle valve 18 is also closed by the coolant pressure, while the bypass valve 15 integrated with the main valve 12 is fully opened. Thus, the coolant drawn from the outlet 21 of the water jackets 20 does not pass through the radiator 22. The coolant is circulated by the water pump 28 through the junction J of the first passage 24, bypass passage 31, housing 27, and inlet 29 of the water jackets 20 as indicated by arrows. Thus, the temperature of the coolant in the housing 27 quickly rises.
However, since the coolant in the radiator 22 and the thermostat cap 26 is not circulated, the temperature rising rate of the coolant temperature B therein is slow. Therefore, as shown in a record of FIG. 8, after even if the temperature A at the point A' becomes 87.degree. C. which is an opening temperature of the main valve 12, the temperature B at the point B' is merely 45.degree. C. There is a difference of 42.degree. C. between the temperatures A and B.
When the main valve 12 of the thermostat 1 opens, the coolant of a low temperature is drawn from the lower outlet 25 of the radiator 22 and fed to the thermostat housing 27 through the second passage 30. Consequently, the temperature B of the coolant at the point B' is further lowered by 13.degree. C. As a result, the difference between the temperature B of the coolant in the passage 30 and the temperature A of the coolant in the housing 27 increases to 55.degree. C. The area of the part shown by the hatching indicates energy loss in the period. It will be understood that the time of the abscissa indicates the elapse from the time at 60.degree. C. of the temperature A.
Since the heat sensitivity of the thermostat 1 is low, the response of the thermostat delays with respect to the change of the coolant temperature. Therefore, the main valve 12 opens after the temperature has become considerably higher than the predetermined opening temperature 87.degree. C. When the main valve 12 opens, the temperature of the coolant is lowered. The main valve 12 closes after the coolant temperature has considerably decreased lower than a predetermined closing temperature. Then, the coolant temperature rises. Namely, there is a large heat overshoot in control of the coolant temperature, so that the main valve is repeatedly opened and closed. When the main valve 12 closes, a surge pressure occurs at the upstream of the main valve.
The heat overshoot causes cracks of the cylinder block and cylinder head of the engine, and the surge pressure causes breakdown of the thermostat 1 and the radiator 22.
Since, mentioned in above, the jiggle valve mechanism is sources of energy loss and engine troubles, the jiggle valve mechanism is removed from the present thermostat in the present invention. And a small hole is formed in the flange of the thermostat. Therefore, pressures applied to the outer side and inner side of the main valve become equal to each other. The spring constant of the return spring is reduced. As a result, the lift up rate is increased in a low temperature range. Furthermore, the thickness of the seal spool is extremely thin (thickness of between 25% and 5% of the diameter of the actuating rod), so that the pressure of the wax for the lift up of the valve is reduced.
FIG. 4 is a diagram showing the lift with respect to the coolant temperature. A line X is the lift of the valve of the present invention and the line Y is the lift of the conventional valve. The reference W shows a lift of the bypass valve 15. The range of the steep curve line is the solid wax state.
The main valve of the conventional valve Y opens at 72.degree. C., the lift at the end temperature 87.degree. C. of the solid wax state is merely 9.6 mm. Thereafter, the lift up rate reduces because of the liquid wax state, and when the lift becomes 12 mm, the coolant temperature reaches such a high temperature as 123.degree. C.
The main valve of the present invention also opens at 72.degree. C., the lift becomes 6 mm by a small temperature increase of 9.degree. C. When the lift reaches 12 mm, the coolant temperature is 85.degree. C. as shown by the line X, which is only increase of 4.degree. C. The coolant temperature of 85.degree. C. is within the range of the solid wax state.
When the automobile mounting the thermostat of the present invention is driven at 80 Km/h, the coolant temperature increases to 77.5.degree. C. However, when the speed reaches to 150 Km/h, the coolant temperature decreases to 70.5.degree. C., because the radiator is cooled by a strong wind. Therefore, the cooling system is provided such that the cooling fan starts at an upper limit temperature of 81.degree. C. and stops at 75.degree. C.
The line Z'-Z of FIG. 4 shows the upper limit of 81.degree. C. The hatched area shows the difference between the flow rate of the coolant passing the main valve of the present invention and the flow rate in the conventional valve. The lift of the line X at 81.degree. C. is 6 mm and the lift of the line Y is 3 mm. Therefore, the flow rate of X is two times as much as the flow rate of Y.
The flow rate at the lift of 6 mm of X which is in the solid wax state corresponds to the flow rate at the lift of 12 mm of Y which is included in the liquid wax state. Thus, the thermostat of the present invention uses only 50% of the own power at the lift of 12 mm. Therefore, even if an automobile mounting the thermostat of the present invention is driven at 150 Km/h, there remains the power of 50%.
However, the conventional thermostat of the line Y enters the liquid wax state range after 86.degree. C. (lift 9.3 mm), where the lift increasing rate largely decreases. The coolant temperature of 37.degree. C. (123.degree. C.-86.degree. C.) is consumed in vain in the period from the lift 9.3 to 12 mm. The thermostat of the present invention demonstrates a double power with half of source, remaining power of 50%.
The coolant flowing through a small hole on the flange needs not worry about taking a longer warm up period for a idling because the cold start fuel injector is provided in the throttle body controlled by a computer compensate a time loss for a idling.
In the cooling system using the thermostat of the present invention, when the coolant temperature exceeds 81.degree. C., the cooling fan operates. Since the flow rate of the coolant at 81.degree. C. is the double of that of the conventional thermostat, the coolant temperature quickly decreases. Therefore, the coolant temperature is kept 81.degree. C.
The upper limit for the cooling fan is not limited to 81.degree. C. It is desirable to set the temperature to an effective value as low as possible dependent on tests.
The high coolant temperature of the conventional thermostat causes various problems such as an increase of fuel consumption and aggravation of the emission.